A new approach to therapy of myocardial ischemia involves the perfusion of oxygenated blood via the venous side of the heart through the coronary sinus and large cardiac veins. Retrovenous diastolic myocardial perfusion (RVDP) has the potential for maintaining myocardial viability in the presence of coronary artery occlusion, acute myocardial ischemia, and during therapeutic interventions such as percutaneous transluminal balloon angioplasty (PCTA), enzyme dissolution of thrombi, coronary angiography, and for myocardial protection until revascularization surgery. RVDP with oxygenated blood has been shown experimentally to: 1) provide 45% of the normal coronary blood flow and, 2) salvage up to 36% of myocardium after coronary ligation in primates. Feasibility of an RVDP system has been clearly demonstrated in Phase I work and a prototype system developed. A sheep myocardial injury model for testing RVDP with sensitive functional and pathologic evaluation methodologies is operational. The difference between perfusion of blood retrovenously and coronary sinus balloon occlusion (blood redistribution) on myocardial salvage will be determined. Complete RVDP systems - control, driving, alarms, and catheters - will be fabricated, durability and in vivo tested. This research will refine the technology and demonstrate the safety and efficacy of RVDP for salvage of ischemic myocardium for widespread clinical application.